9 Honors Biology Midterm Vocabulary

Matter

anything that has mass and takes up space

Element

pure substance made of one type of atom

Atom

smallest unit of an element

Compound

substance made of two or more elements chemically combined

Molecule

two or more atoms bonded together

CHNOPS

Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur

Trace elements

elements needed in very small amounts (iron, iodine, zinc)

Proton

positively charged particle in nucleus

Neutron

neutral particle in nucleus

Electron

negatively charged particle in electron cloud

Atomic number

number of protons

Atomic mass

protons + neutrons

Bohr model

shows electron shells

Lewis dot diagram

shows valence electrons

Valence electrons

outer shell electrons

Ion

charged atom (lost or gained electrons)

Isotope

atoms of same element with different neutrons

Isomer

same molecular formula, different structure

Chemical bond

attraction between atoms

Covalent bond

sharing electrons

Nonpolar covalent bond

equal sharing of electrons

Polar covalent bond

unequal sharing of electrons

Ionic bond

attraction between oppositely charged ions

Electronegativity

ability to attract electrons

Hydrogen bond

weak attraction between partial charges

Chemical reaction

breaking/forming bonds

Reactants

starting materials

Products

ending materials

Energy

ability to do work

Polarity

uneven charge distribution

Hydrogen bonding

attraction between water molecules

Cohesion

water sticks to water

Adhesion

water sticks to other substances

Surface tension

resistance at water's surface

Specific heat

ability to resist temperature change

Evaporative cooling

cooling as water evaporates

Density

mass per volume

Solute

substance being dissolved

Solvent

substance doing the dissolving

Solution

mixture of solute + solvent

pH scale

measures acidity/basicity

Acidic

more H⁺ ions (pH < 7)

Basic (alkaline)

more OH⁻ ions (pH > 7)

Neutral

equal H⁺ and OH⁻ (pH = 7)

Buffer

resists pH change

Homeostasis

maintaining internal balance

Organic compound

contains carbon

Carbon skeleton

chain/ring of carbon atoms

Monomer

building block molecule

Polymer

chain of monomers

Dehydration synthesis

builds polymers by removing water

Hydrolysis

breaks polymers using water

Carbohydrate

sugars and starches

Monosaccharide

simple sugar (glucose)

Disaccharide

two sugars (sucrose)

Polysaccharide

complex carb (starch)

Isomers

same formula, different structure

Starch

plant energy storage

Glycogen

animal energy storage

Cellulose

plant cell wall

Chitin

exoskeletons & fungal cell walls

Lipid

hydrophobic molecules

Triglyceride

glycerol + 3 fatty acids

Fatty acid

long hydrocarbon chain

Saturated fat

no double bonds, solid

Unsaturated fat

double bonds, liquid

Phospholipid

membrane lipid

Hydrophilic

water-loving

Hydrophobic

water-fearing

Steroid

lipid with 4 fused rings

Cholesterol

steroid precursor & membrane component

Protein

folded polypeptide with function

Amino acid

protein monomer

Polypeptide

chain of amino acids

Peptide bond

bond between amino acids

R group

variable side chain

Primary (1°) structure

amino acid sequence

Secondary (2°) structure

alpha helix, beta sheet

Tertiary (3°) structure

overall 3D shape

Quaternary (4°) structure

multiple polypeptides

Denaturation

loss of structure/function

Enzyme

protein catalyst

Nucleic acid

stores genetic information

DNA

deoxyribonucleic acid

RNA

ribonucleic acid

Nucleotide

monomer of nucleic acids

Phosphate group

Pentose sugar

deoxyribose or ribose

Acetyl CoA (acetyl coenzyme A)

A two-carbon molecule formed from pyruvate that enters the citric acid cycle.

Alcohol fermentation

An anaerobic process that produces ethanol and CO₂ and regenerates NAD⁺ so glycolysis can continue.

ATP synthase

An enzyme that makes ATP as hydrogen ions flow through it during chemiosmosis.

Cellular respiration

The process by which cells break down glucose to make ATP using oxygen.

Chemiosmosis

The movement of hydrogen ions across a membrane that powers ATP production.

Citric acid cycle (Krebs cycle)

A series of reactions that breaks down acetyl-CoA to release CO₂ and high-energy electrons.

Electron transport chain (ETC)

A series of proteins that transfer electrons and use their energy to pump hydrogen ions.

FAD⁺

An electron carrier that accepts electrons and hydrogen ions.

FADH₂

The reduced form of FAD⁺ that carries high-energy electrons to the electron transport chain.

Glycolysis

The first step of cellular respiration that breaks glucose into pyruvate and makes ATP.

Intermediates

Molecules formed during the steps of a metabolic pathway.

Kilocalorie (kcal)

A unit of energy commonly used to measure food energy.